The present disclosure relates generally to the utilization of a pre-sintering cycle to a green additive core that will allow the core to be self-supportive during the firing process.
Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor section to pressurize an airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases.
Gas turbine engine hot section components such as blades and vanes are subject to high thermal loads for prolonged time periods. Other components also experience high thermal loads such as combustor, exhaust liner, blade outer air seal, and nozzle components. Historically, such components have implemented various air-cooling arrangements that permit the passage of air to facilitate cooling. In addition, the components are typically provided with various coatings such as thermal barrier coatings to further resist the thermal loads.
The internal passage architecture may be produced through various processes such as investment cast, die cast, drill, Electron Discharge Machining (“EDM”), milling, welding, additive manufacturing, etc. Investment casting is a commonly used technique for forming metallic components having complex geometries, especially hollow components, and is used in the fabrication of superalloy gas turbine engine components.
A primary mechanism in which to cool turbine gas path components is to utilize a series of in-wall channels to pass cooling air that is typically several hundreds of degrees colder than the gas path. These walls are typically cast-in to the airfoil and involve designs that distribute cooling air throughout the entirety of the part. The air is subsequently ejected either through film holes or other leakage apertures to the external flowpath environment. The traditional method of fabricating gas path components is to utilize an investment casting process that forms an interior core for the cooling channels. This core is typically a weak ceramic whose strength is significantly less than the component material. This material weakness has allowed for highly quality castings since the core typically collapses or ‘crushes’ during the solidification process.
The advancement of additive manufacturing to manufacture components provides for extremely detailed, intricate, and adaptive feature designs. The ability to utilize this technology not only increases the design space of the parts but allows for a much higher degree of manufacturing robustness and adaptability. However, the current state-of-the-art in additive manufacturing does not allow for the creation of single crystal materials due to the nature of the process to be built by sintering or melting a powder substrate to form. It is however advantageous for the development die-less cores or the integration of cores and shells for use in the casting process.
A part of processing the additive cores is to burn out the additive manufacturing binder material and sinters the particles together. During this process, the green additive core is placed within an oven and heated. The development of the heating cycle is such that experimentation is conducted to figure out how the cycle should be performed to retain the geometric shape of the part and eliminate sag or deflection of the part. To retain the shape of green cores during the firing process, secondary ceramic parts (typically called setters) are typically created and used to support the core within the chamber. The inclusion of these setters, along with the delicate nature of the cores, may result in significant costs within the development of a new core design.